Courseiva
← 200-301
Full test
Switching and Network Access →hardTroubleshootingObjective-mapped

CCNA Switching and Network Access Practice Question

Exhibit

R1#show running-config | section interface GigabitEthernet0/0
interface GigabitEthernet0/0
 no ip address
 duplex auto
 speed auto
!
interface GigabitEthernet0/0.10
 encapsulation dot1Q 10
 ip address 192.168.10.1 255.255.255.0
!
interface GigabitEthernet0/0.20
 encapsulation dot1Q 10
 ip address 192.168.20.1 255.255.255.0
!
R1#show interfaces trunk
Port        Mode         Encapsulation  Status        Native vlan
Gig0/0      on           802.1q         trunking      1

Port        Vlans allowed on trunk
Gig0/0      1-1005

Port        Vlans allowed and active in management domain
Gig0/0      1,10,20

Port        Vlans in spanning tree forwarding state and not pruned
Gig0/0      1,10,20

R1#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks
C       192.168.10.0/24 is directly connected, GigabitEthernet0/0.10
     192.168.20.0/24 is variably subnetted, 2 subnets, 2 masks
C       192.168.20.0/24 is directly connected, GigabitEthernet0/0.20

You are connected to R1. The network uses a router-on-a-stick design with a single switch (SW1) and two VLANs (10 and 20). Currently, hosts in VLAN 10 cannot ping hosts in VLAN 20, and the trunk between R1 and SW1 shows a native VLAN mismatch. Examine the provided configuration and output, then apply the necessary corrections to R1 so that inter-VLAN routing works correctly.

⚠ Common exam trap

Candidates often forget to enable 'ip routing' globally, assuming it is on by default. They may also overlook the native VLAN mismatch or incorrectly use a Layer 2 switchport command instead of 'encapsulation dot1Q 99 native' on the router interface.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Change the native VLAN on R1's trunk interface to 99, correct the encapsulation on G0/0.20 to dot1Q 20, and enable IP routing globally.

The configuration has three issues: 1) The native VLAN on the trunk is VLAN 1, but the switch expects VLAN 99 (common mismatch scenario). 2) Subinterface G0/0.20 uses encapsulation dot1Q 10 instead of 20, causing VLAN 20 traffic to be mis-tagged. 3) The 'ip routing' command is missing globally, so R1 cannot route between subinterfaces. To fix, configure the main interface G0/0 with 'encapsulation dot1Q 99 native' to set the native VLAN to 99, correct the encapsulation on G0/0.20 to 'dot1Q 20', and enable IP routing with 'ip routing'.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✓

    Change the native VLAN on R1's trunk interface to 99, correct the encapsulation on G0/0.20 to dot1Q 20, and enable IP routing globally.

    Why this is correct

    This is correct because it addresses all three issues: the native VLAN mismatch (switch expects VLAN 99, R1 uses VLAN 1), the misconfigured subinterface encapsulation (VLAN 20 traffic tagged as VLAN 10), and the missing 'ip routing' command required for inter-VLAN routing.

  • ✗

    Change the native VLAN on R1's trunk interface to 99, correct the encapsulation on G0/0.20 to dot1Q 20, but do not enable IP routing because it is enabled by default.

    Why it's wrong here

    This option is incorrect because the assertion that IP routing is enabled by default on Cisco routers is false. Inter-VLAN routing over subinterfaces requires the global command 'ip routing' to be explicitly configured; by default, a Cisco router will not forward packets between its subinterfaces. Without this command, the router drops packets destined for other VLANs, so even with correct VLAN 99 native and dot1Q 20 encapsulation fixes, inter-VLAN communication remains broken.

  • ✗

    Change the native VLAN on R1's trunk interface to 1, correct the encapsulation on G0/0.20 to dot1Q 20, and enable IP routing globally.

    Why it's wrong here

    This option fails to resolve the native VLAN mismatch on the trunk link. The switch is configured with native VLAN 99, so R1's trunk interface must also use native VLAN 99; leaving R1 on native VLAN 1 means untagged frames on the trunk are interpreted differently by each device, causing spanning-tree and traffic misbehavior. While the encapsulation on G0/0.20 and global IP routing are correctly addressed, the unchanged native VLAN mismatch still disrupts trunk operation and prevents proper inter-VLAN forwarding.

  • ✗

    Change the native VLAN on R1's trunk interface to 99, correct the encapsulation on G0/0.10 to dot1Q 10, and enable IP routing globally.

    Why it's wrong here

    This option mistakenly modifies G0/0.10 instead of the actually misconfigured G0/0.20 subinterface. The problem statement indicates that VLAN 20 traffic is being tagged with VLAN 10, so the encapsulation on G0/0.20 must be changed from dot1Q 10 to dot1Q 20. Correcting G0/0.10 to dot1Q 10 does not fix the tagging error on G0/0.20, leaving VLAN 20 clients unable to communicate with the router or other VLANs.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.

✓Change the native VLAN on R1's trunk interface to 99, correct the encapsulation on G0/0.20 to dot1Q 20, and enable IP routing globally.Correct answer▾

Why this is correct

This is correct because it addresses all three issues: the native VLAN mismatch (switch expects VLAN 99, R1 uses VLAN 1), the misconfigured subinterface encapsulation (VLAN 20 traffic tagged as VLAN 10), and the missing 'ip routing' command required for inter-VLAN routing.

✗Change the native VLAN on R1's trunk interface to 99, correct the encapsulation on G0/0.20 to dot1Q 20, but do not enable IP routing because it is enabled by default.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that IP routing is not enabled by default; it requires the 'ip routing' global command.

Why candidates choose this

Candidates may assume that a router automatically routes between interfaces, but in Cisco IOS, routing must be enabled globally.

✗Change the native VLAN on R1's trunk interface to 1, correct the encapsulation on G0/0.20 to dot1Q 20, and enable IP routing globally.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that the native VLAN must match on both sides; changing R1's native VLAN to 1 does not match the switch's native VLAN 99.

Why candidates choose this

Candidates might think that native VLAN 1 is the default and acceptable, but the switch has been configured with native VLAN 99, so R1 must match that.

✗Change the native VLAN on R1's trunk interface to 99, correct the encapsulation on G0/0.10 to dot1Q 10, and enable IP routing globally.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that the subinterface G0/0.20 is associated with VLAN 20, so its encapsulation must be dot1Q 20, not 10.

Why candidates choose this

Candidates might confuse the VLAN IDs or think that correcting the native VLAN is sufficient, but the subinterface encapsulation must match the VLAN it serves.

Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”

Visual reference

Switch VLAN 10 Sales (192.168.10.0/24) PC-A PC-B VLAN 20 HR (192.168.20.0/24) PC-C PC-D Router VLANs isolate traffic — inter-VLAN routing requires a Layer 3 device

About these practice questions

One of 1,389 original 200-301 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →

How Courseiva writes practice questions · Editorial policy

JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.